One can look at a software project and be dismayed at the number of problems it may have. Code quality is difficult to quantify but in general, readability, ease of maintainability and few basic bugs could be some of the things which indicate code quality.
One way to begin improve code quality is by beginning to clean up the code. One approach could be to employ the boy scout principle as a programming practice:
The Boy Scouts have a rule: “Always leave the campground cleaner than you found it.” If you find a mess on the ground, you clean it up regardless of who might have made the mess. You intentionally improve the environment for the next group of campers.